Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers, capacitance increases. To address this problem, insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide (and other materials that have a relatively high dielectric constant) to form the dielectric layer that separates the metal lines.
One material that may be used to form such a low k dielectric layer is carbon doped oxide. Using this material instead of silicon dioxide to separate metal lines may yield a device having reduced propagation delay, cross-talk noise, and power consumption. Carbon doped oxides have been prepared by plasma enhanced chemical vapor deposition ("PECVD") using gases that provide a source of silicon, oxygen, and carbon. Examples of source gases that have been used included dimethylmethoxysilane and alkyl silanes such as methylsilane, trimethylsilane, and tetramethylsilane. While these source gases produce carbon doped oxides having acceptable k values, it would be desirable to produce carbon doped oxides having even lower k values.